<form name="frmBuscaCliente" id="frmBuscaCliente" method="post" action="" onsubmit="return false;">
    <table>
        <tr>
            <td width="25">Nome: </td>
            <td width="240"><input name="txtNome" id="txtNome" type="text" style="width: 220px" /></td>
            <td width="25"><input type="submit" name="btBuscar" id="btBuscar" value=" " onclick="Lista('txtNome', 'tdRetornoCliente');" /></td>
        </tr>
        <tr>
            <td id="tdRetornoCliente" align="center" colspan="3">
                <select name="cmbListaClientes" id="cmbListaClientes" style="width: 290px;" size="16"></select>
            </td>
        </tr>
    </table>
</form>